1. Field of the Invention
The present invention relates to differential amplifier circuitry formed on a semiconductor substrate. In particular, the present invention relates to differential amplifier circuitry formed on a semiconductor substrate with a rewiring technique.
2. Description of the Prior Art
FIG. 12 shows a circuit diagram of high-frequency differential amplifier circuitry according to a prior art (See Japanese Patent Laid-Open Publication No. JP-2003-133862-A). Referring to FIG. 12, the high-frequency differential amplifier circuitry is configured by transistors Q1 and Q2, a bias circuit 103, resistors 104 and 105, pads 201, 203 and 204, CSP (Chip Size Package) output terminals 205, 207 and 208, and input terminals IN1 and IN2. The transistors Q1 and Q2 constitute a differential pair of the differential amplifier circuit. The bias circuit 103 generates a predetermined bias current, and supplies the bias current to a base of the transistor Q1 via the resistor 104 and to a base of the transistor Q2 via the resistor 105 so as to control the biased states of the transistors Q1 and Q2, respectively. The CSP output terminal 205 is connected with emitters of the transistors Q1 and Q2 via the pad 201 and a parasitic inductance L1. The CSP output terminals 207 and 208 are connected with collectors of the transistors Q1 and Q2 via the pads 203 and 204, respectively.
In the high-frequency differential amplifier circuitry according to the prior art configured as described above, when differential signals are inputted to the respective bases of the transistors Q1 and Q2 via the input terminals IN1 and IN2, the respective differential signals amplified by the differential pair, which is constituted by the transistors Q1 and Q2, are outputted from the collectors of the transistors Q1 and Q2 via the output terminals 207 and 208.
However, due to the parasitic inductance component L1 caused by rewiring to form the above-mentioned high-frequency differential amplifier circuitry according to the prior art on a semiconductor substrate, the emitters of the transistors Q1 and Q2 come into a common impedance state, which generates a higher-harmonic wave having frequencies, such as two times, three times and the like, as high as that of the differential signals inputted to the emitters of the transistors Q1 and Q2. Thus, a problem is created in that the higher-harmonic wave interferes with input signals and deteriorates distortion characteristics of the differential amplifier circuitry.
An additional problem is created in that the resistors 104 and 105 for biasing the bases of the transistors Q1 and Q2 attenuate the input signals, which causes a gain reduction.
Furthermore, in the case of forming the high-frequency differential amplifier circuitry on one chip with a modem circuit part and a frequency synthesizer part, there is still a further problem in that signals from the respective circuits interfere with one another via a semiconductor substrate, which causes characteristic deterioration such as generation of spurious signals and deterioration of noise and the like. For example, in the case of forming a transmission driver amplifier on one chip with the modem circuit part and the frequency synthesizer part, the frequency of the oscillator might be shifted when an output signal of the transmission driver amplifier leaks into and interferes with the oscillator. Otherwise, carrier leakage might occur when a local oscillation signal, inputted to a modulator, directly leaks into the transmission driver amplifier, which causes deterioration of modulation accuracy.